Blog · Controls and audit
How duplicate supplier payments happen, and how to stop them
Most duplicate payments aren’t fraud. They happen when one purchase gets recorded twice somewhere between the quote and the bank: two requests, two invoices, two orders or two supplier records. The fix is a short chain of checks, each placed where a duplicate first appears: a quote reference checked when the request is raised, one record per supplier, approval recorded before anything is ordered, a purchase order number on every invoice, and a final check by accounts payable before money leaves.
Why duplicates are hard to spot
A duplicate payment rarely looks wrong. Each document is real, the supplier delivered something, and every invoice was approved by someone with the authority to approve it. The problem is that two people each saw half the picture, and nobody saw both halves together.
Many suppliers notice and send the money back. Not all do, and small amounts can sit unnoticed on a supplier account until someone reconciles a statement, or never. The earlier in the purchase a duplicate is caught, the less work it takes to undo.
Five ways the same purchase gets paid twice
These are the patterns that come up again and again in small and mid-sized teams.
- The same quote raised by two people. A site manager and an office buyer both ask for the same quote to be ordered. Two orders go out, and the supplier either delivers twice or invoices twice for one delivery.
- A resent invoice with a new number. The supplier reissues an invoice, perhaps to correct an address or as a reminder, and gives it a new number. A check on invoice numbers alone won’t see it.
- A pro forma and a final invoice both paid. A pro forma is paid up front to release the goods. The final tax invoice arrives weeks later and is processed as a new bill.
- A purchase order revised and the old one still open. The price or quantity changes, so a new order is issued, but the first is never cancelled. Each order can now attract an invoice of its own.
- A supplier set up twice. “Acme Supplies” and “Acme Supplies Ltd” sit side by side in the supplier list. Duplicate checks usually run within one supplier record, so an invoice entered under each name passes both.
The controls, in the order they bite
Each control sits at the point where a particular kind of duplicate is created. Put them in this order and most duplicates are stopped before an invoice exists at all.
- Check the quote reference when the request is raised. Ask for the supplier’s quote number on every request and compare it with earlier requests. Two people asking for the same quote find out about each other before anything is approved.
- Keep one record per supplier. Let one person, or one short onboarding step, add new suppliers. Search before adding, and check the registration number, VAT number and bank details against existing records rather than the name alone.
- Record approval before the order. Every order should come from one approved request, and nothing should be ordered on a verbal yes. A purchase that was never approved has no record to compare a later invoice against.
- Require a purchase order number on every invoice. Say so on the order and in your terms: an invoice without an order number goes back to the supplier. The invoice then ties to one order, and a second invoice against an order that’s already been invoiced in full stands out. When an order is revised, cancel the old one so only one stays open.
- Check before payment. Accounts payable looks for near matches, not just exact ones: the same supplier and amount within a few weeks, the same order number on two invoices, a final invoice that follows a paid pro forma. This is also where three-way matching sits, if you do it.
Cause and control at a glance
Most teams already do one or two of these. Your gaps are the causes in the left-hand column that nothing in your process would catch.
| How it happens | Control that catches it | When it bites |
|---|---|---|
| Same quote raised by two people | Quote reference checked against earlier requests | When the request is raised |
| Supplier set up twice | One supplier record, checked on registration and VAT number | When the supplier is added |
| Order placed with no record behind it | Approval recorded before the order | Before the order goes out |
| Old order left open after a revision | Cancel the superseded order, so one order stays open per purchase | When the order is revised |
| Resent invoice with a new number | Order number required on every invoice | When the invoice arrives |
| Pro forma and final invoice both paid | Accounts payable check for near matches | Before payment |
What to do when you find one
Finding a duplicate is not a disaster. Most suppliers will refund or credit the money once they see the evidence, because it isn’t theirs to keep.
- Confirm it’s a real duplicate. Check that both payments cover the same goods or the same work, not two genuine deliveries that happen to share an amount.
- Write to the supplier. Give both invoice numbers, both payment dates and the order number, and ask for a refund or a credit note.
- Choose refund or credit. A refund is cleaner if you buy from them rarely. A credit note suits regular suppliers, but record it against their account so it’s actually used on the next invoice.
- Correct the VAT. If the input VAT on the duplicate invoice was claimed, it may need correcting on your return. Confirm the treatment with your accountant.
- Fix the cause. Work out which of the five patterns it was, and tighten that control rather than adding another review on top of everything.
Most of the work happens before the invoice
It’s tempting to treat duplicates as an accounts payable problem, because that’s where the money leaves. But four of the five controls above sit on the purchasing side, before an invoice exists. Accounts payable is the last check, not the only one.
A team that raises every purchase as a request, records who approved it and issues one numbered order for it gives accounts payable something solid to check against. Without that record, the person paying the invoice is guessing.
Questions
What is a duplicate supplier payment?
It’s paying a supplier more than once for the same goods or services. It usually comes from the same purchase being recorded twice, as two requests, two invoices, two orders or two supplier records, rather than from fraud.
How do you find duplicate payments you’ve already made?
Reconcile supplier statements against your payments, and look for credits on the supplier’s side you don’t recognise. Then sort payments by supplier and amount and look for near matches close together in time, not just identical invoice numbers.
Does a purchase order stop duplicate payments on its own?
Not on its own. It helps when every invoice must quote the order number and someone checks that the order hasn’t already been invoiced in full. A revised order also needs the old one cancelled, or there are two orders to invoice against.
Can a supplier keep a duplicate payment?
In practice most suppliers refund or credit it once they see the evidence. If one won’t, put the request in writing with both invoices and payments, and take advice from your accountant or adviser before going further.